A KC will average half a swing better in the same amount of time than a Ridill/KC.
A KC will average a very slight fraction better than a KC/M.Kris
However those numbers assume no dualwield gear, adding in a suppa means the KC/M.Kris becomes a touch better, adding both a suppa and Augmented Nuevo pushes it to about half of a swing. Ridill still loses with those extra.
It's the smallest of direct upgrades, and it does not take into account the bonuses you can get from /drg and/or the 30 HP shield.